Copolymers from octafluoronaphthalene

ABSTRACT

A method for polymerizing octafluoronaphthalene and the resulting perfluorocompounds prepared therefrom. Polymerization is accomplished by reacting the octafluoronaphthalene monomer with a mono or difluoroxyperfluoroalkane.

STATEMENT OF GOVERNMENT INTEREST

The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.

This is a division, of application Ser. No. 182,562, filed Aug. 29, 1980, now U.S. Pat. No. 4,321,359.

BACKGROUND OF THE INVENTION

This invention relates to novel perfluoropolymers and to methods for their preparation. In a more particular aspect, this invention concerns itself with methods for the polymerization of octafluoronaphthalene and to the novel compounds prepared thereby. The resultant reaction products are useful in a wide variety of electrical, chemical and aerospace applications. They are inert, low melting solids with thermal stability as well as excellent adhesivness to glass and untreated Teflon and metal surfaces. They can also be used as precursors in the synthesis of polyfunctional fluorocarbons.

The present interest in the utilization of fluorocarbon compounds for a number of industrial applications has spawned a considerable research effort in an attempt to provide new compounds and novel routes of synthesis. For example, it is known that elemental fluorine will homopolymerize hexafluorobenzene and pentafluoropyridine to mainly a hexafluorocyclohexadienyl liquid oligomer and a perfluoroazacyclohexadienyl glassy solid respectively. The copolymerizability of bis(fluoroxy) difluoromethane with perfluoroaromatic (C₆ F₆), perfluoro-N-heteroaromatic (C₅ F₅ N), and parabonded perfluoroaromatic (Dewar C₆ F₆) is also known. The purpose was to interpose stable --OCF₂ O-- linking groups between six-membered ring moieties. For example, moieties were generated from copolymerizing with hexafluorobenzene, with pentafluoropyridine, and with hexafluorobicyclo [2.2.0] hexa-2,5-diene. These copolymers, however, did not form simple alternate microstructures due to concurrent fluorination and pendant perfluoro-1,3-dioxolane ring formation.

In an attempt to overcome this problem, the research effort referred to above, was maintained and it was unexpectedly discovered that even more interesting and useful products could be synthesized by effecting the polymerization of octafluoronaphthalene by reacting it with mono-and difluoroxyperfluoroalkanes. It was found that the octafluoronaphthalene monomer could be readily homopolymerized in the presence of monofluoroxyperfluoroalkane CF₃ OF and copolymerized with difluoroxyperfluoroalkane, CF₂ (OF)₂ through aromatic nuclear addition reactions.

SUMMARY OF THE INVENTION

The present invention concerns itself with the polymerization of octafluoronaphthalene and to novel aromatic nuclear addition reactions. These reactions take place between the octafluoronaphthalene monomer and a monofluoroxyperfluoroalkane to produce a homopolymer; and between the monomer and a difluoroxyperfluoroalkane to produce a copolymer. The resulting perfluorobicyclic compounds provide new and useful products which are inert, low melting perfluoropolymer solids with thermal stability. They exhibit moiety unsaturation between carbons common to both rings which provide cross-linking sites. This makes them especially useful as precursors in the synthesis of polyfunctional fluorocarbons. The novel C₁₀ F₈ -CF₂ (OF)₂ copolymer also exhibits good adhesion to glass and untreated Teflon and metal surfaces.

Accordingly, the primary object of this invention is to provide routes for the synthesis of perfluorobicyclic polymers.

Another object of this invention is to provide for the polymerization of octafluoronaphthalene by effecting aromatic nuclear addition reactions between the octafluoronaphthalene monomer and a mono or difluoroxyperfluoroalkane.

Still another object of this invention is to provide for the synthesis of novel perfluorobicyclic compounds that are especially useful as precursors because they exhibit unsaturation only between the carbons common to both rings.

The above and still other objects and advantages of this invention will become more readily apparent upon consideration of the following detailed description of its preferred embodiments.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with this invention it has been found that the above-mentioned objects can be accomplished by effecting the solution polymerization of monomeric octafluoronaphthalene (C₁₀ F₈) in the presence of a mono or difluoroxyperfluoroalkane. The polymerization of C₁₀ F₈ is accomplished by adding CF₃ OF or CF₂ (OF)₂ at a mole ratio of about 1:2 or 1:3. This yields an almost quantitative glassy solid without fragmentation of C₁₀ F₈. The C₁₀ F₈ homopolymer is linked by carbon-to-carbon bond of the C₁₀ moieties, which contain pendant trifluoromethoxy groups. On the other hand, the copolymer is linked by --OCF₂ O-- linking groups between the C₁₀ moieties as well as carbon-to-carbon bonds. The latter C₁₀ moieties contain the pendant perfluoro-1,3-dioxolane rings. The bulk of these polymers retain double bonds between the carbons common to both rings.

The invention is further shown by the following examples which depict specific embodiments thereof.

EXAMPLE I

Octafluoronaphthalene (4.0 g, 14.7 mmole), perfluoro-2-butyltetrahydrofuran solvent (25 ml), and a magnetic stir bar encapsulated in Teflon TFE were placed in a Pyrex reaction vessel which was attached to a copper vacuum line, evacuated at -196° C., warmed to ambient temperature, and stirred to a white suspension. CF₃ OF (47.0 mmole) was slowly added with stirring at room temperature for 6 hr and progressively warmed to 100° C. for 2 hr. At that time, the solution absorption of CF₃ OF ceased. The suspension turned to a clear liquid during the initial phase of CF₃ OF addition at room temperature. Then a sequence of color changes was observed from clear yellowish, pinkish, greenish, and back to clear yellowish solution, which was evacuated at 100° C. to give a clear glassy solid of almost quantitative yield. The volatile condensate in the liquid-nitrogen-cooled trap was analyzed by infrared spectroscopy to consist mainly of the inert solvent in the presence of a small amount of carbonyl fluoride and silicon tetrafluoride. This volatile mixture was not investigated further. The residual solid flowed at a temperature below 50° C. with glass transition temperature at -2° C. and softening temperature at 11° C. and was soluble in hexafluorobenzene and perfluoro-2-butyltetrahydrofuran. The microstructure of the homopolymer, indicated as A in Table I was elucidated by ¹⁹ F-NMR. The isolated double bonds between the carbons common to both rings showed a weak absorption at 1680 cm⁻¹.

The following structural formula illustrates the homopolymer of this example ##STR1## wherein n is an integer of from 2 to 20

EXAMPLE II

A procedure similar to that shown in Example I was used to copolymerize, except CF₂ (OF)₂ (30.0 mmole) was added to C₁₀ F₈ (3.5 g, 12.8 mmole) to give a clear yellowish transparent solid of almost quantitative yield. The resulting copolymer indicated as C in Table I flowed at a temperature below 100° C. with glass transition temperature at 10° C. and softening temperature at 28° C. and was soluble in hexafluorobenzene and perfluoro-2-butyltetrahydrofuran. Its microstructure was elucidated by ¹⁹ F-NMR. The precopolymer B, (Table I) was the precursor of copolymer C, before the absorption (or pressure drop) of CF₂ (OF)₂ above the polymer solution had stopped. The molecular weight of the clear liquid precopolymer B was about 2000. The double bond between the carbons common to both rings showed a weak absorption at 1680 cm⁻¹ end its conjugated double bonds at 1850 and 1755 cm⁻¹. After the complete addition of 30 mmole of CF₂ (OF)₂, the residual copolymer C was a clear yellowish glassy solid with reduced unsaturation compared to the precopolymer B. The melted copolymer C was sticky and exhibited thermal stability with no detectable volatile products at 250° C.

The copolymer of this example is illustrated by the following structural formula ##STR2## wherein n is an integer from 2 to 30.

Table I, presented hereinafter, summarizes the ¹⁹ F-NMR data of the homopolymer (A) of Example 1 and copolymer (C) of Example 2.

                                      TABLE I                                      __________________________________________________________________________     .sup.19 FNMR Data of C.sub.10 F.sub.8 Polymers                                           Polymer   Chemical                                                                               No. of Fluorines                                             Group and Shift (ppm from                                                                        in Polymer Group                                   Polymer   Assignment                                                                               CFCl.sub.3)                                                                            Measured*                                                                            Theoretical**                                __________________________________________________________________________     C.sub.10 F.sub.8CF.sub.3 OF homopolymer-A                                                 ##STR3## 54.4 87-160                                                                            85.8 73.9                                                                            90 82                                                   ##STR4## 185-205 8.5   16                                           C.sub.10 F.sub.8CF.sub.2 (OF).sub.2 precopolymer-B                                        ##STR5## 52-56   10    10                                                     OCF.sub.2 O                                                                              50.5    3.5   4                                                       ##STR6## 92- 144 34    38                                           C.sub.10 F.sub.8CF.sub.2 (OF).sub.2 precopolymer-D                                        ##STR7## 144-158 4.5   6                                                       ##STR8## 168-200 3     4                                            C.sub.10 F.sub.8CF.sub.2 (OF).sub.2 copolymer-C                                           ##STR9## 52-62   10    10                                                     OCF.sub.2 O                                                                              50.5    8.2   8                                                       ##STR10##                                                                               92-144  5.8   52                                                      ##STR11##                                                                               168-200 5.4   4                                            __________________________________________________________________________      *Relative area.                                                                **Based on suggested homopolymer A, where n = 1, precopolymer B and            copolymer C.                                                             

The bis(fluoroxy)difluoromethane was prepared in a conventional manner such as that shown in Hohorst and Shreeve, J. Am. Chem. Soc., 89, 1809 (1967). The fluoroxytrifluoromethane and octafluoronaphthalene were purchased from PCR and perfluoro-2-butyltetrahydrofuran (FC-75) was purchased from 3M. The compounds were checked by infrared spectroscopy and used as received.

Vacuum manipulations were carried out in a copper-Monel system with a Pyrex reaction vessel. Pressures were measured with a Hoise gauge (0-100 cm Hg absolute with 500 increments) of accuracy to 1 mm Hg. The amount of volatile reactant was determined by P-V-T measurements assuming ideal gas behavior.

The infrared spectra were measured on a Perkin-Elmer 567 spectrophotometer. NaCl windows were used for the liquids and solids and a 5-cm Monel gas cell fitted with AgCl windows for the gases. The ¹⁹ F-NMR spectra were recorded by a Varian XL-100 spectrometer operating at 94.1 MHz and 35° C. using hexafluorobenzene as an external reference. The F chemical shifts were then converted to CFCl₃ as the reference using the value of 164.9 ppm for hexafluorobenzene.

Fluoroxytrifluoromethane and bis(fluoroxy)difluoromethane are potentially hazardous, although they do not appear to be sensitive to phase changes. Adequate protection shielding and caution must be practiced.

Upon oxidation of the C₁₀ F₈ homopolymer of Example 1 with CF₃ OF and the C₁₀ F₈ copolymer of Example 2 with CF₂ (OF)₂ preferably under alkaline conditions, perfluoropolyethers containing tertiary hydroxyl groups are formed. This is illustrated by the following equations in which equation (1) illustrate the oxidation of the homopolymer (A) of Example 1 and equation (2) illustrates the oxidation of the copolymer (B) of Example 2. The letter n represents an integer of from 2 to 20 in equation 1 and from 2 to 30 in equation 2. ##STR12##

Example 3 and 4 which follow, further illustrate the oxidation of the polymers of Examples 1 and 2.

EXAMPLE 3

The homopolymer (A) of Example 1 (4.0 g) was dissolved in about 20 ml of perfluoro-2-butyltetrahydrofuran and the solution was added slowly to a stirred solution to KMnO₄ (1.0 g) in anhydrous acetone (50 ml) during 30 min. The mixture was stirred overnight at room temperature. Water (20 ml) was added and stirred for two hours. The perfluoro-2-butyltetrahydrofuran layer was separated from the top aqueous layer, which was then extracted with fresh perfluoro-2-butyltetrahydrofuran solvent. The combined perfluoro-2-butyltetrahydrofuran extracts was evacuated at ambient temperature to give a clear yellowish solid of almost quantitative yield. Upon exposure to air, the yellowish solid was hygroscopic and darkened to a brownish black solid, polymer having the formula shown in equation (1) as polymer (C). The infrared analysis of the polymer showed the absence of olefinic bonds and the presence of hydroxyl groups.

EXAMPLE 4

The polymer shown in equation 2 was oxidized from the copolymer (B) of Example 2 by a similar procedure to that in Example 3. The yellowish residual solid from copolymer (B) was likewise hygroscopic and darkened to a brownish black solid shown as polymer (D), which contained hydroxyl groups in the absence of olefinic bonds.

The polymers (C) and (D) of Examples 3 and 4 can also be prepared by bubbling ozone (3 to 5% in oxygen) through the perfluoro-2-butyltetrahydrofuran solutions of the polymers (A) and (B) of Examples 1 and 2 respectively.

While the invention has been described with particularity in reference to specific embodiments thereof, it is to be understood that various alterations and modifications thereof may be undertaken and that all such modifications as fall within the scope of the appended claims are intended to be included herein. 

What is claimed is:
 1. As a compound, the copolymer having the formula ##STR13## wherein n is an integer of from 2 to
 30. 2. A method for preparing a perfluorobicyclic polymer which comprises the steps of (A) forming a reaction mixture of (1) octafluoronaphthalene and (2) bis(fluoroxy) difluoromethane in a mole ratio of about 1:2 to 1:3; (B) heating said mixture within a vacuum for a period of time of about six hours at room temperature and progressively warming said mixture to 100° C. for about two hours to effect a reaction therebetween; and (C) separating the resulting copolymer. 